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Summary of experimental report of basic amplifier circuit 1 1. Understand the working principle and design method of multistage direct coupling amplifier circuit.
2. Familiar with the design method of high gain multistage direct coupling amplifier circuit.
3. Master the test method of multistage amplifier performance index.
4. Master the method of introducing negative feedback into the amplifier circuit.
Second, the experiment preview and thinking
What are the coupling modes of 1. multistage amplifier circuit? What are their characteristics?
2. Using the direct accidental mode, the operating point of each amplifier will gradually increase, which will eventually lead to the failure of the circuit. How to solve this problem from the circuit structure?
3. Design tasks and requirements
(1) Basic requirements
A multistage amplifier is designed with given transistors 2SC 18 15(NPN) and 2SA10/5 (PNP). Given that VCC =+ 12V and -VEE =- 12V, it is necessary to design the emitter current IEQ3 of the differential amplifier constant current source. The unreal voltage gain of single-ended input and single-ended output of differential amplifier is at least greater than 10 times, and the undistorted voltage gain of main amplifier is not less than 100 times; The double-ended input resistance is greater than10Ω, the output resistance is less than10Ω, and the DC points of the input stage and the output stage are guaranteed to be zero. Design and simulation.
Third, the experimental principle
The main task of direct-coupled multistage amplifier circuit is to imitate the equivalent internal structure of operational amplifier OP07, simplify some circuits, and design a multistage amplifier with high voltage gain by using differential input, * * * injection amplification, complementary output and other structural forms, which can amplify large and small signals without distortion.
1. input stage
The input stage of this circuit is a constant current differential amplifier circuit using NPN transistors. Differential amplifier circuit has little zero drift in DC amplification, and is often used as the front stage of multistage DC amplifier circuit to amplify smiling DC signal or AC signal.
The working configuration of typical differential amplifier circuit is double-ended input and double-ended output. The two sides of the amplifier circuit are symmetrical, the two transistors have the same model and characteristics, and the corresponding resistors have the same resistance. The rejection ratio of the * * * mode of the circuit is very high, which is beneficial to anti-interference. When the circuit is used as the input stage of multi-stage amplifier circuit, it adopts the working configuration of vi 1 single-ended input and uo 1 single-ended output. Calculate the static operating point: the two ends of the differential amplifier circuit are symmetrical, here let T 1, and the current parameters of T2-related emitter and collector are IEQ 1=IEQ2=IEQ, ICQ 1=ICQ2=ICQ. Let UB 1=UB2≈0V, then Ue≈-Uon, and calculate ICQ3 of T3, that is, 2 times IEQ equals 2 times ICQ.
Here, the transmitter adopts a constant current circuit composed of a stable operating point circuit, and here is a relatively simple method for determining the operating point:
Because IC3≈IE3, it is only necessary to determine IE3, IE3 UR4UE3 (VEE) and R4R4.
VCC ( VEE)) R5 Uon R5 R6
Gain of Uo 1 when using uo 1 single-ended input and uo 1 single-ended output.
2. Main amplifier stage (RC//rlrlrl (p//)1rbrber1rbe.
This stage amplifier adopts the * * * amplifier circuit of the first stage PNP transistor. Because the experimental circuit adopts direct coupling, the working points at all levels influence each other. The NPN transistor is used in the differential amplifier circuit of the previous stage, and the collector voltage Uc 1 of the output terminal uo 1 has increased, which is also the base DC voltage of the second stage amplifier. If the amplifier stage continues to use NPN emitter amplifier circuit, the working point of the collector will increase and the resistance value of the collector will be poorly designed. If it is very small, the magnification will be insufficient. If it is large, the collector resistance will be poor. In this case, complementary transistors are generally used to design, that is, the amplifier circuit of the second stage is designed with PNP transistors. In this way, when working in the amplification state, the collector potential of NPN tube is higher than the base potential, while the collector potential of PNP tube is lower than the base potential. After matching with each other, the operating points of the front and rear stages can be conveniently configured, so that the main amplifier can work at the best operating point and the maximum amplification factor can be designed without distortion.
As the reference circuit of the intermediate main amplifier stage, PNP transistor is connected to the differential input stage, in which T4 is the main amplifier, and its static operating points UB4, UE4 and UC4 are determined by P 1, R7 and P2.
The differential amplifier circuit and the amplifier circuit are directly coupled, and their operating points influence each other. The simple estimation method is as follows:
, UC4 VEE IC4 RP2 UE4 VCC IE4 R7, UB4 UE4 Uon UE4 0.7 (silicon tube)
Due to the interaction of UB4 UC 1, the specific details should be carefully determined during debugging. The output gain AU2 of the amplifier stage in this circuit.
3. Output stage circuit
The output stage adopts complementary symmetrical circuit, which improves the output dynamic range and reduces the output resistance.
T4 is the main amplifier tube, and its collector is connected with D 1 and D2, which overcomes the cross distortion of complementary symmetry between T5 and T6. The circuit at this stage is not amplified.
Fourth, the test method
The design results are simulated by Multisim, and the circuit parameters are adjusted to meet the performance requirements. All the simulation results are given.
The circuit diagram is as shown in figure 1, UO2 RC UO 1RBRBBE.
Analog circuit diagram
Figure 1 Measurement of static working point:
The static operating points IEQ3 and IEQ4 are obtained through testing, as shown in Figure 2, which meet the design requirements.
Figure 2 Static working point measurement
Input and output terminal voltage test:
Test the single-ended input and single-ended output waveforms of the differential amplifier as shown in Figure 3. The input voltage is VPP=4mV, the output voltage is VPP = 5 1.5mv, and the magnification of the differential amplifier is about 12.89 times. The magnification meets the requirements.
Fig. 3 waveform diagram at low voltage The input and output waveforms of the main amplifier stage are shown in fig. 4.
Fig. 4 waveform diagram of input and output of main amplifier stage
As shown in the figure, the input voltage is VPP=5 1.5mV, the output voltage is VPP=6.75V, and the magnification is 13 1.56 times. The input and output voltage test of the whole circuit is shown in the figure.
Fig. 5 input and output waveform diagram of multistage amplifier circuit
The input voltage is VPP=4mV, the output voltage is VPP=4.29V, and the magnification is 1062 times. The experimental conclusions are as follows:
In this circuit, the differential amplifier circuit is used to effectively suppress zero drift, the PNP transistor amplifier stage is used to realize the main amplifier circuit, and the complementary symmetrical output circuit is used to eliminate the influence of cross distortion. A multistage amplifier circuit is designed and tested. The amplification factor is greater than 1000, and the circuit works stably.
Abstract of experimental report of basic amplifier circuit 2 Experiment 1: Design and simulation of instrumentation amplifier.
I. The purpose of the experiment
1. Master the design method of instrumentation amplifier.
2. Understand the ability of instrumentation amplifier to suppress * * * mode signals.
3. Be familiar with the debugging method of instrument amplifier.
4. Master the use methods of testing analog circuit instruments in the virtual instrument library, such as oscilloscopes, millivoltmeter signal generators and other virtual instruments.
Two. Experimental principle
Instrumentation amplifier is a high-precision amplifier used to amplify the difference signal. It has a large * * * mode rejection ratio, extremely high input resistance, and the gain can be adjusted in a wide range. The schematic diagram of the instrumentation amplifier is as follows:
The instrumentation amplifier consists of three integrated operational amplifiers. U3 forms a subtraction circuit, that is, a differential amplifier. U 1 and U2 each form a symmetrical noninverting amplifier for their corresponding signal sources, with R 1=R2, R3=R5 and R4=R6. Let R 1=R2=R, then
VO2—VO 1 =( 1+2R/Rg)(Vi2—VI 1)
U3 is the standard weighted subtractor, and Vo 1 and Vo2 are its input signals, and its corresponding output voltage VO =—(R6/R5) VO2+R4/(R3+R4) VO1(kloc-0/+R6/R5).
Since R3=R5=R4=R6=R, therefore
VO = VO 1—Vo2 =( 1+2R/Rg)(VI 1—Vi2)
Differential voltage gain of instrumentation amplifier
AVF = Vo/(VI 1—Vi2)= 1+2R/Rg
Therefore, changing the resistance value can change the differential voltage gain of the instrumentation amplifier, which is positive.
Three. Experimental content
1. Build the instrumentation amplifier according to the above schematic diagram, and the specific indicators are as follows:
(1) When the input signal UI = 2 sinwt (MV), the output voltage signal UO = 0.4 sinwt (MV), Avf=200, and f= 1kHz.
(2) the input impedance requires ri >；; 1mω
2. Use the virtual instrument library to test the analog circuit instruments and debug them according to the design index.
3. Record and analyze the data.
Four. experimental procedure
Connect the circuit according to the following figure, and set up a function signal generator, which outputs sine with frequency of 1kHz and amplitude of 2 mV; Observe the waveform changes with an oscilloscope.
Where Avf= 1+2R/Rg≈200, and the input differential mode signal 2mV meets the experimental requirements.
Experimental results of verbs (abbreviation of verb)
As shown in the figure, the oscilloscope CH 1, CH2 and CH3 are Vi 1, Vi2 and Vo respectively. As can be seen from the figure, the output Vo=0.4sinwt(V) is in phase with Vi 1.
Experience of intransitive verb experiment
From this experiment, I learned the basic operation method of multisim, understood the principle of instrument amplifier, and became more familiar with the functions of some common circuit components through simulation experiments.